dt-bindings: net: ethernet-controller: add QUSGMII mode

Add a new QUSGMII mode, standing for "Quad Universal Serial Gigabit
Media Independent Interface", a derivative of USGMII which, similarly to
QSGMII, allows to multiplex 4 1Gbps links to a Quad-PHY.

The main difference with QSGMII is that QUSGMII can include an extension
instead of the standard 7bytes ethernet preamble, allowing to convey
arbitrary data such as Timestamps.
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/ethernet-controller.yaml

@@ -67,6 +67,7 @@ properties:
       - gmii
       - sgmii
       - qsgmii
+      - qusgmii
       - tbi
       - rev-mii
       - rmii